Rinse-added fabric softener compositions are well-known. Typically, such compositions contain a water-insoluble quaternary-ammonium fabric softening agent. Commercially available fabric softening compositions are basically aqueous dispersions of the water-insoluble quaternary compounds. Quaternary ammonium compounds with long chain alk(en)yl groups interrupted by carboxy groups (i.e., biodegradable quaternary ammonium) are known, from e.g. French Patent No. 1.593.921. Concentrated softening compositions containing such rapidly biodegradable quaternary ammonium are disclosed in European Patent No. 0 040 562.
However, since these compounds are intended to be marketed as aqueous dispersions, and since the rapidly biodegradable quaternary ammoniums are more subject to hydrolysis than the conventional (DTDMAC-type) cationic softening agents, such rapidly biodegradable softening compositions can enounter hydrolytic stability problems upon prolonged shelf storage.
It is therefore an object of the present invention to provide aqueous softening compositions containing rapidly biodegradable quaternary ammonium compounds, which are sufficiently shelf stable.
Indeed, it has been found that, by keeping the pH of the compositions herein in a certain range, lower than what is currently used in rinse-added softening compositions, excellent hydrolytic stability is ensured on prolonged shelf storage.